Analysis of a course of lectures : on mechanics, hydrostatics, pneumatics, and astronomy / read by James Ferguson.

  • James Ferguson
Date:
1761
Catalogue details

Licence: Public Domain Mark

Credit: Analysis of a course of lectures : on mechanics, hydrostatics, pneumatics, and astronomy / read by James Ferguson. Source: Wellcome Collection.

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    ti S ] the wedge, as it generally does, the velocity of the refiftance on each lide is to the velocity of the power adfing on the wedge* as half the thicknefs of the wedge is to the whole length of the cleft. And in this cafe, the power and refiftance balance each other, when the power is to the refiftance, as half the thick¬ nefs of the wedge (when it is driven quite into the wood) is to the whole length of the cleft below the back of the wedge. The ferew may be confidered as if it were an in¬ clined plane wrapt round a cylinder-, hence, the power muft turn the cylinder quite round, in the time that the weight or refiftance moves through a fpace equal to the diftance between the fpirals or threads of the ferew. Therefore, the velocity of the power is in proportion to the velocity of the weight or refiftance, as the circumference of a circle deferibed by the power, in one turn of the ferew* is to the diftance between the fpirals of the ferew: and the power and refiftance balance each other. When the former is to the latter, as the diftance between the fpirals is to the circumference of the circle de¬ feribed by the power.—This machine, befides the advantage proper to itfelf, has generally the benefit of the wheel and axle, on account of the handle or lever by which it is turned. As the ferew includes the inclined plane, and two equally inclined planes make the wedge, we have all the mechanical powers combined together in a common jack, if it be turned by the fly: for then, we have alfo the lever, the wheel and axle, and the pullies.—If this machine be made ufe of for raifing a weight, by a power applied to the fly, the power will balance the weight, if it be in proportion to the weight* as the velocity of the weight is to the velocity of the fly*, Now, confidering how faft the fly moves with refpedb to the motion of the weight, it is evident that a crafie * conftruft^d in the manner of a common jack, would
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